The present invention relates to flame retardant additives for organic polymers, and in particular phosphorus-sulfur flame suppressant additives.
Flame suppressant additives are commonly added to polymer products used in construction, automotive, electronic, electrical laminate, wire and cable, textile and other applications. FR additives increase the limiting oxygen index (LOI) of polymer systems, allowing articles made from those polymer systems to pass standard fire tests. Various low molecular weight (<˜1500 g/mol) brominated compounds are used as FR additives for organic polymers. Many of these, such as hexabromocyclododecane and polybrominated diphenylethers, are under regulatory and public pressure that may lead to restrictions on their use, and there is an incentive to find a replacement for them.
Various phosphorus compounds have been used as FR additives. These include organic phosphates, phosphonates and phosphoramides, some of which are described in U.S. Pat. Nos. 4,070,336 and 4,086,205, as well as in “The Chemistry and Use of Flame Retardants”, J. W. Lyons, Chapter 2: Chemistry of Fire Retardants Based on Phosphorous p. 29-74 (1987). Another commercially available FR additive is 2,2′-oxybis[5,5-dimethyl-1,3,2-dioxaphosphorinane 2,2′-disulfide], which has the structure:
These compounds tend to provide moderate ignition resistance, and are generally not as effective as hexabromocyclododecane or other brominated FR additives.
It is desirable to provide an alternative FR additive for organic polymers, and for foamed polymers in particular. The FR additive should be capable of raising the LOI of the polymer system when incorporated into the polymer at reasonably low levels. Similarly, the FR additive should be capable of conferring good fire extinguishing properties to the polymer system, again when present at reasonably small levels. Because in many cases the FR additive is most conveniently added to a melt of the organic polymer, or else (or in addition) is present in subsequent melt processing operations, the FR additive should be thermally stable at the temperature of the molten polymer. This is typically in the range of 150° C. or higher, and is often above 220° C. It is preferable that the FR additive has low toxicity.